1. Field of the Invention
This invention relates to an improved system for warning travelers following a vehicle when the vehicle is traveling at a speed below a predetermined reference speed.
2. Prior Art
In certain situations, particular motor vehicles do not maintain the same speed as other motor vehicles on the roadway. This can occur, for instance, when heavy trucks climb a long incline on a highway without enough power to maintain highway speeds. Often in this situation, the truck operator will manually activate the flashing hazard lights or "flashers" to warn those following him that the vehicle is slow moving. Similarly, when a vehicle is slow moving due to disrepair or due to the operator purposely driving slowly to look for a particular street address, etc., the vehicle operator will often manually activate the flashing hazard warning lights to warn that the vehicle is slow moving.
The applicant is aware of several patents generally relating to the subject matter of this invention. U.S. Pat. No. 4,800,377, to Slade, discloses a system for actuating rear warning lights on a vehicle when the vehicle speed falls below a predetermined lower limit or threshold speed. Slade uses a magnetic pick-up to generate a pulsed signal correlating to the speed of the vehicle. This pulsed signal is compared to a reference pulse signal representing the threshold speed and, if the pulsed signal is below the reference signal, rear warning lights are flashed to warn those following the vehicle. The Slade patent provides a mechanism for enabling the operator to adjust the threshold speed if the vehicle is in slow speed conditions (city driving).
GB 2,175,462, to Hepburn, discloses a warning system that provides a visual warning whenever the vehicle is decelerating. The Hepburn patent also uses a pulsed signal to represent the speed of the vehicle.
U.S. Pat. No. 4,162,445, to Cambell, and U.S. Pat. No. 4,368,427, to Hayashi, both disclose digital speedometers. The Cambell patent uses optically generated timing pulses with a rate proportional to the rotational speed of the speedometer cable driver. The speedometer of the Hayashi patent includes a hysteresis processing circuit to improve the response of the system.
U.S. Pat. No. 3,691,525, to McClellan et al., discloses a speedometer wherein the vehicle speed is indicated to those located remotely from the vehicle through a series of lights mounted on the vehicle.
U.S. Pat. No. 3,790,932, to Ridpath, discloses a braking warning device for vehicles that is particularly adapted for snowmobiles and other vehicles that do not normally have brake lights. The Ridpath patent uses a variable output rotary generator for producing a voltage that is proportional to the vehicle speed. This voltage is compared with itself over time and is used to illuminate an external light when the vehicle is decelerating. A light is also illuminated when the speed of the vehicle falls below a predetermined rate.
U.S. Pat. No. 3,805,161, to Bayhz et al., discloses a system for sensing the speed of a motor vehicle. A pick-up coil device is used which generates an AC signal having a frequency related to the speed of the vehicle. The Bayhz et al. patent further discloses that the sensed speed may be used to provide a visual indication when a certain maximum vehicle speed is attained.
Most motor vehicles are operated in both low-speed environments (city driving) as well as high-speed environments (highway driving). While a device that automatically flashes warning lights whenever the vehicle speed is below a predetermined threshold speed is desirable in highway driving, it is often unwelcome and unnecessary in city driving when the vehicle is often being operated below the threshold speed. Thus, this is a drawback of the prior art.
A further drawback of the prior art systems is that on many vehicles, the turn signals utilize the same lights as the warning light system and when the warning lights are flashing, it is not possible for the driver to indicate a change of vehicle direction.